Choosing an Anchorage: The Four Questions

Once you know how your anchor bites (recall holding ground and scope from the last card), the skipper's next job is where to drop it. A good anchorage answers four questions in order: holding ground, shelter, swing room, and depth.

First, holding ground — the seabed itself. Mud and firm sand hold well; rock, shingle, and weed are notoriously poor because the anchor skates or fouls instead of digging in. Your chart tells you: 'M' means mud, 'S' sand, 'Wd' weed. Second, shelter — you want land or a breakwater upwind of you, so the fetch (the distance wind travels over open water) stays short and waves stay small. Crucially, forecast the wind overnight, not just now: a cove that shelters a westerly can become a dangerous lee shore if the wind backs to the east.

Third, swing room. A boat at anchor pivots around its anchor as wind and tide shift, sweeping a full circle of radius equal to your deployed rode. With 30 m of chain out you sweep a ~60 m circle — so you must sit far enough from other boats, moorings, and shallows that the whole circle stays clear. Boats on chain and boats on rope swing differently, so leave extra margin.

Fourth, depth — with tide. Charted depths are usually below chart datum (roughly the lowest tide), so you must check the state of the tide now and at low water tonight. If you need 3 m to float and the tide will drop 2 m before dawn, you must anchor where there's at least 5 m now — or wake up aground.